The UK television series QI delights in exposing facts you have always believed as being untrue.  And very entertaining it is.  If they are reading this, here is another one for them.  Which country first used gas in the First World War?  I was absolutely convinced it was the Germans.  But it turns out that it was in fact the French.  It’s understandable that this hasn’t been remembered.  The attack was so ineffective that the Germans didn’t even realise that gas had been used.

The Germans at least managed to get their enemies to notice when they resorted to using gas. They were desperate to break the stalemate on the Western Front, and this overcame their reluctance.  But even so, they found the results disappointing.  The army that in the end used the most gas was the British – mainly due to the geography.  It happened that the prevailing wind was in their favour.  But even for the British it proved to be of questionable value.  A lot of efforts were devoted to chemical warfare on both sides, but it never justified the investment.   It might even have saved lives – by diverting resources into inefficient gas attacks perhaps fewer were available for weapons that did kill people.

The whole premise behind gas warfare turned out to be false.  Far from being deadly, gas turned out a lot easier to handle than everyone thought.  Counter measures quickly emerged.  Standing up for example.  Chlorine is heavier than air so remaining upright reduced exposure considerably.  It is also very soluble in water, so a wet cloth over the mouth was pretty effective.  In the end, its value turned out to be the fear it induced rather than the effects that it had.  After the war international agreements were made to limit the deployment of chemical weapons.  Although gas had inflicted relatively few casualties, the image of a soldier wearing a gas mask became the iconic image of the horror of war.  The international community failed to address war, fascisim and genocide but was able to agree that none of them liked chemical weapons.

If we were rational creatures we would be a lot more worried by explosives than poisons.  It is a sight easier and quicker to blow somebody up than to poison them.  But there is something about chemicals that induces a level of fear that simple  death by dismemberment can’t compete with.  The fear induced by gas warfare worked because of this chemophobia.  And chemophobia is still with us.  I was a bit surprised to realise that I am a pretty convinced chemophobe myself.  This was brought home to me the other day when I was trying to work out what effect pesticides in your food might have.  The risks of pesticides is something that I have been interested in for a long time.  The increase of the world’s population has been the most striking feature of the age we live in.  I was born in 1960 when the population was 3 billion.  Today is nearly 7 billion.  But really the most amazing thing about it is that so many more people are actually able to not only eat, but eat better than anyone in previous generations would have dreamed of.

This is thanks to the green revolution in agricultural techniques, and pesticides have played a large part in this.  Without them there would be a lot fewer people about and many more of those that did survive would be hungry.  But there is no such thing as a free lunch.  Pesticides are by their nature harmful.  That is what they are used for – to cide the pests.  So it isn’t surprising that there is some payback in the form of increased levels of diseases resulting from the use of pesticides.  Or that at any rate was what I thought. We can drive the hardest bargain with nature we can, my reasoning went, by being careful in our choice of agents, but ultimately we have to pay for all this abundant food with an increased risk of long term diseases,  principally cancer.

We’ve eaten the dinner.  What is the bill?  One of the first serious attempts to assess it was made by Doll and Peto, two guys who should know what they are talking about.  Richard Doll did one of the most convincing studies that established the link between smoking and lung cancer and Richard Peto has a long career in studying incidence of cancer.  They published a study in 1981 of the main causes of cancer in the US which is still well worth a look at.  When it comes to causes of cancer, tobacco and diet carry off the prize, accounting for 65% between them.

Pesticides were found by Peto and and Doll to be such a small risk that they couldn’t find any direct evidence that they caused cancer at all.  When I read that not very long after it came out, I was really surprised and rather suspicious.  I reasoned that some of the incidences had been conflated with their estimates for general pollution, which they estimated as being responsible for 2% of all cancer cases.  Also, cancer can take a very long time to develop.  Pesticides had only been in use for a couple of decades when most of the data Peto and Doll were working on was generated. Pesticide use was on the up, and more and more data was being collected.  I made the assumption that half the cancer that Peto and Doll attributed to general pollution would turn out to be down to pesticides.  The evidence would emerge with time, and the surprisingly low figure of 1% that I assumed would no doubt be revised upwards.

Well nearly thirty years later I am still waiting.  I don’t routinely read the literature in this area, and it occurred to me that by now my personal estimate was likely to have been justified by new information.  So I have just had a look at all the evidence I can find.  It was a long search.  It turns out that while studies of the possible carcinogenic effects of particular chemicals in labs are numerous, looking at how cancer actually occurs in real life is much rarer.  But I did manage to come up with one interesting one looking at fruit growers in Kashmir.  Kashmiri fruit growers get brain cancer at the same rate as people in the same population that aren’t directly exposed.  But they get it worse, and their survival rates are lower – 12% die compared to 5%.  There might be other explanations but it does look a lot like the exposure to pesticides makes their cancer worse.  Unfortunately, multiple pesticides are used which muddies the water a lot.  Interestingly it does fit in with a 1998 paper that picked up a possible link between pesticide exposure and development of brain cancer in french farm workers.  This paper was suggestive rather than conclusive because it relied heavily on statistical inferences, and you really need a bit more than that.  If you did enough studies you would find all sorts of spurious relationships between one thing and another.  But put together with the Kashmiri study and you might begin to see a pattern starting to emerge.

On the other hand it isn’t very sensible to concentrate on only one particular form of cancer in isolation.  A review of pesticide operatives in Florida shows that they are generally healthier than the rest of the Florida population.  Their overall rate of cancer is lower, but there are a couple of types of cancer where they have higher levels.  One study can’t be the basis of any firm inferences, but you might conclude that there may be something going on.  Perhaps pesticides have an effect of cancer, but it isn’t a clear cut and obvious one.

But that is about it.  Farm workers are likely to be the people who are going to suffer the worst effects of pesticides, and what little hard data we have suggests that they are more likely to be prone to a couple of specific cancers but on the whole have lower levels of cancer generally.  This is not hugely decisive because the outdoor farming lifestyle has lots of other things that make it unusual apart from exposure to pesticides.  Look at the general population and the evidence that links pesticide use to incidence of cancer just isn’t there.  And it isn’t just me that has looked.

Although there isn’t a lot of data on the link between pesticides and cancer, there are plenty of reviews.  I have included a couple int the references to give a flavour.  A paper done by scientists at Dow Chemicals concluded that there was no evidence of a link.  I suppose you might expect them to reach that conclusion, but that doesn’t necessarily make them wrong.  Another review from an environmental science department emphasises the potential risks and points out how important it is to study the issue.  They are no doubt right.  But they cannot point to any clear cut evidence of harm.  Remember, pesticides have been in widespread use since the fifties.  That is over half a century.

My personal assumption that about 1% of cancer deaths were attributable to pesticide use turns out to be without foundation.  So how did I feel on making this discovery?

At first I couldn’t believe it.  Of course pesticides cause cancer, everyone knows that.  I was quite annoyed about it in fact.  It wasn’t that I was opposed to the use of pesticides.  I was quite prepared to defend their use.  I had some great arguments lined up.  And I was quite pleased with myself for my maturity.  ‘Of course a lot of people complain about the harm pesticides do, without considering all the good they do…’  You can imagine.  But it turns out that pesticides don’t have an Achilles Heal in the form of long term cancer risk.  Later I calmed down and realised that I was being incredibly selfish. It is of course good news that pesticides don’t cause cancer, even if it leaves me with some redundant arguments.

So why was I so resistant to what is basically good news?

I am not alone in this. I have a feeling most people would be surprised to learn that there is no strong evidence linking pesticides with an increased risk of getting cancer. And I have feeling that most people don’t realise that cancer rates are decreasing. I have a feeling that the notion that cancer is on the increase goes back to Rachel Carson’s Silent Spring.  It really is difficult to exaggerate the influence of that ground breaking book on the development of the environmental movement. Rachel Carson spoke about an ever increasing level of cancer, and asked what the cause of it was.  She didn’t know the answer and didn’t claim to.  She was always too fastidious a scientist to make statements she couldn’t back up.  But I think it was clear enough that that was she thought given that she devoted so much space to it in a book principally concerned with pesticide use.

At the time, she could easily have been right.  The cancer that killed Carson herself was leukemia.  The incidence of leukemia was increasing during the period she was writing the book as she must have known very well.  She had to face the grim prognosis both for herself and for future generations.  It must have been hard to come to terms with.  It is a shame she didn’t live to see what happened next.  Almost as soon as she died the figures for leukemia started to fall.  Silent Spring was influential, but it didn’t lead to an overnight halt to use of pesticides.  Whatever was responsible for the rise and subsequent fall of leukemia incidence, a fall that is continuing, it can’t have been pesticides.

But the interesting question is why so many of us are so attached to the idea that synthetic pesticides are carcinogenic.  It is an idea that has persisted for decades in the absence of any supporting evidence.   I can almost precisely work out how long I have believed it. I first remember reading about the issue around the time of the Queen’s 25th Jubilee in 1977 and finally worked out I had it wrong a couple of weeks ago.  That is 34 years of thinking the world is a more dangerous place than it actually is.

I can’t help thinking that like the world war one generals who continued to think that their gas attacks were more deadly than they really were despite the evidence to the contrary, those of us who have persisted in believing in the risky nature of pesticides suffer from an irrational fear of chemicals.  It seems strange to identify myself as a chemophobe when I make a living as a chemist, but there it is.

The interesting question is why so many of us find it so easy to be scared by chemicals.  I think I may know the answer.  It goes back to our evolutionary history.  We are the descendants of people who lived in an environment that was full of very real risks.  We had to contend not just with wild animals intent on eating us, but also no end of poisonous plants and fungi that could end our lives just as effectively.  The humans that survived were the ones that were both fleet footed and cautious.  The ones that were heedless of the dangers all around them were the ones that didn’t leave any offspring behind them.

The cost of missing out on a few harmless tasty treats is a lot lower than the cost of eating something poisonous and dying.  So the optimum strategy is playing it safe and being automatically suspicious or anything new.  We still judge things this way.

This is reflected in the structures of our brain.  We do our thinking and reasoning in the pre-frontal cortex, a rather small bit toward the front of the brain.  But a lot of our behaviour is controlled by the limbic system which occupies a much bigger region further back. The limbic system is what we use to assess dangers, and when activated it tends to override most of our other brain functions.  This is why it is hard to think when you are scared.  Fear is a powerful emotion precisely because it operates directly on the part of our brain that has the most direct effect on our actions.  Its role is to spot dangers and react to them, and it is constantly on the look out for things that might be a threat.


When we lived as hunter-gatherers this made a lot of sense.  Nowadays, thanks to our technology and culture we have succeeded in eliminating a great many of the dangers we used to experience.  But we still have all the circuitry that we used to need ticking away on the look out for things to react to.  We have a sort of danger deficit.  And I think this is where chemophobia comes in.  We are hard wired to live in a world of unquantifiable risk, and chemicals neatly fit the bill.  We used to live surrounded by poisonous plants, so we are predisposed to think that the unfamiliar taste or odour might kill us.  Chemists have unwittingly contributed to this by deciding to derive chemical names from latin and greek sources.  This adds another layer of strangeness and unfamiliarity.  You rational pre-frontal cortex might be quite relaxed about whether you call it water or dihydrogen oxide, but your much  more powerful limbic system doesn’t think things like that through.

Chemophobia is basically a function of the way our brains evolved in a world that is very different to the one we live in now. On the whole it is probably a good thing.  We don’t face anywhere near as  many dangers as we used to, but the world isn’t completely safe even now.  But it is worthwhile being aware of the way we process fear.  We don’t have to worry about sabre toothed tigers or deadly berries any more, but we do have to watch out for other humans.

Playing on our fears is a favourite trick of marketeers.  It is almost the only trick of spammers, scammers and scare mongers.  Watch out for adverts and sales pitches that are aimed directly at your limbic system.  You don’t have to look far for examples in the beauty world.   (You were probably wondering when I was going to get back on topic.)  Not to pick on this particular company, who are certainly not the worst, but this bare Escentuals advert is a typical example.  They just happened to be open in another window on my browser while I was writing this.  The classic example, which probably is the worst, is the Story of Cosmetics video.  This dispenses with facts entirely and devotes itself to ten minutes of limbic system manipulation aimed at scaring the life out of you – or at least at scaring a donation out of you.


My feeling is that when I see someone trying to scare me, I am scared.  Scared that I haven’t yet spotted how they are trying to get the money out of my pocket.  The trouble is it is remarkably hard to avoid  being influenced by direct appeals to the brains defence mechanisms.  We are sometimes not even conscious of the impact it is having. Here are a few ways to avoid being taken in.  Watch out for emotive language.  In particular non-specific threats like ‘nasties’ or ‘dirty dozen’ are usually a sign somebody is trying to emotionally manipulate you.  Recognise it and label it as such in your head.  (This is quite a good way of dealing with emotional manipulation generally – give it a try next time someone is giving you a hard time.)  If you can redirect your fear into dislike of the people who are trying to put one over on you, that is good too.  Remember that really knowing what is going on is much the safest way to live.  And outwitting the scare mongers feels good too.

[hana-code-insert name=’General Interest’ /]


There is now a wikipedia entry on Chemophobia

Doll and Peto’s 1981 study of the causes of cancer in the United States

Kashmir Farmers and Brain Cancer

Viel JF, Challier B, Pitard A, Pobel D. Brain cancer mortality among French farmers: The vineyard hypothesis. Arch Environ Health. 1998;53:65–70. [PubMed]

Dow Chemical Review Paper

Occup Environ Med. 1999 Jan;56(1):14-21. Mortality in a cohort of licensed pesticide applicators in Florida.
Fleming LE, Bean JA, Rudolph M, Hamilton K.











6 thoughts on “Chemophobia”

  1. What a mind-bogglingly informative posting Colin. I am blown away by your info on pesticides, and the way you bring in the brain function is just plain worthy of applause. (can you hear me clapping?) Thank you! 🙂

  2. Thanks to both of you for your kind comments. I was a bit worried about pressing the publish button on such a long post so I am glad you liked it.

  3. Hi Colin – thanks for the post – it was good bedtime reading! Interesting angles, however, you make no reference to the Precautionary Principle in your argument – that if something is not proven to be safe (or if there’s any doubt) we should tread carefully with it or avoid it.

    Surely the absence of evidence doesn’t mean there’s no risk? Is 50 years long enough to assess the accumulative effect of our exposure to chemicals, pesticides, toxins, etc?

    1. Yes you have some good points YanarA. The precautionary principle is a good one. The onus should be on the innovator to justify the safety of anything new. But in the case of pesticides the problem they are solving is a pressing one. With a rising world population, if we don’t deploy pesticides we face people going hungry. Pesticides aren’t nice chemicals and they do have harmful effects. My point was mainly that I personally had exaggerated their long time harmful effects for nearly three decades.

      With regard to yet to be identified risks, yes I think that is possible. Had DDT continued to be used it would almost certainly have started causing health problems in humans. DDT still looks pretty safe on paper. If you dig around internet you’ll find people accusing Rachel Carson of being a mass murderer for getting it banned. Their argument is that withdrawing DDT hampered anti-malaria programmes. They are wrong only because they underestimate the potential for it to accumulate. The dose makes the poison. If a material can accumulate in the environment then the dose will continue to increase until it reaches dangerous levels. This is my argument against triclosan. It won’t do you any harm to use a product containing it, but it is building up in the environment. Potentially parabens could do the same looking at their chemical and physical structure, but there isn’t any actual evidence of this happening yet that I know about.

      So I remain highly suspicious of pesticides in general. But most of them don’t accumulate and evidence of them doing harm to end consumers is thin on the ground to say the least. And life spans continue to increase. And it could well be the case that by making fresh fruit and vegetables easier to get hold of, pesticides actually reduce diseases even in countries where people already have enough to eat. It is even possible that by reducing the amount of toxins plants themselves produce in self defence, that fruits and vegetables grown with pesticides are healthier than equivalent organic ones. I don’t personally know of anyone who consciously avoids organic products because they might be carcinogenic, I certainly don’t myself, but they would have just as good a case as the organic advocates.

  4. Pingback: oh dear: not the EWG (1) « The Praise of Folly

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